Make a cream sauce of the butter or margarine, flour, seasonings and milk. Add squash, bread crumbs, onion and slightly beaten egg yolks. Fold into stiffly beaten egg whites and pour into greased ring mold. Set in pan of hot water and cover mold with heavy paper or with foil. Bake in moderately hot oven (475 F.) about 1 hour until set. Remove from water and let stand 5 minutes. Turn out on chop plate. Fill center with small buttered beets. Yield: 8-10 servings.